Plasma processing has continued to evolve as manufacturing companies attempt to stay competitive in the semiconductor industry. To gain a competitive advantage, different methods and arrangements have been implemented to increase the amount of plasma that may be utilized in substrate processing to produce non-defective devices
One development that has shown continuing promise is the use of new and different geometries in plasma processing machines. Different geometries, such as long straight plasma tube and convoluted plasma tube, have been utilized in an attempt to efficiently absorb microwave power or convert absorbed microwave power into useful plasma species. To facilitate discussion, FIG. 1 shows a simple diagram of a prior art convoluted plasma tube assembly. Plasma 112 may be formed within a plasma tube 102 through the coupling of one or more gases (e.g., O2, N2, N2H2, HeH2, water vapor, and fluorinated compounds) with microwave power, which may have been transmitted by a microwave power generator 106 through a waveguide 108. Those skilled in the arts are aware that conventional plasma tube of one inch or less in diameter may lose significant percentage of the microwave power that may be generated due to thermal loading. Since plasma 112 may include both harmful plasma species and useful plasma species, shape and dimension of plasma tubes may be manipulated to allow for harmful species to recombine into useful species. Consequently, different geometries may translate into higher efficiency apparatuses.
Consider the situation wherein, for example, plasma 112 travels through plasma tube 102 and encounters a bend 116. As plasma 112 interacts with walls of plasma tube 102 at bend 116, some of the plasma species may recombine. However, with a convoluted plasma tube, the chance for neutral species to recombine may have also increased. As a result, the more convoluted a plasma tube, the less efficient the plasma tube may be in delivering neutral species to a plasma processing chamber.
To reduce the number of useful plasma species from recombining, some manufacturers may use straight plasma tubes. Without a bend, the recombination rate of plasma species within plasma tube may be reduced. However, manufacturers may have to extend the plasma tube to minimize the possibility of harmful plasma species from reaching the plasma processing chamber.
Additionally, plasma species may be formed outside of the waveguide enclosed area of the plasma tube due to microwave radiation leakage that may occur. Traps have been used in some plasma tube assembly to limit the amount of leakage. Traps are usually hollow aluminum disk shape device, which may measure approximately 0.5 inches to 2 inches thick. However, in practice, not all microwave radiation may be contained and microwave leakage may occur resulting in power loss and an extension of harmful plasma species.
Although the geometry of plasma tubes and traps may provide a partial solution for delivering useful plasma species to plasma processing chamber, what are needed are methods and arrangement for creating a highly efficient downstream microwave plasma system.